1. Field of the Invention
The present invention relates generally to a customized passive hearing protection earplug, a use thereof and a method for manufacturing such an earplug.
2. Description of Related Art
Environmental sounds are typically composed of a mixture of various sound wave frequencies having varying intensities. It is well documented that repeated or prolonged exposure to sounds of sufficiently high sound pressure level will cause temporary or permanent hearing loss, i.e. can damage the auditory organ and cause serious hearing problems, including deafness. Harmful noise such as caused by explosions or bursts are often comprised of a mixture of sound wave frequencies of varying intensity. These disturbing frequencies are in both the high and low frequency bands and have intensity sufficient to cause hearing problems. Individuals who are frequently exposed to such disturbing and sometimes dangerous frequencies and intensities run the risk of incurring such injuries as hearing loss or even deafness. These individuals include workers at demolition or construction sites, operators of heavy, noisy equipment and those in active military service. Ear (i.e. hearing) protection is needed to prevent a loss in hearing acuity and the gradual increase in the threshold of hearing resulting from extended exposures to loud noise.
A large part of the population is exposed to hazardous noise from time to time. This can be at work, whilst traveling, during leisure activities or at home. The exposure can lead to permanent hearing loss, distract people's attention from other hazards or simply cause stress. In order to prevent both accidents and permanent hearing damage, hearing protection devices (HPDs) have been provided in many styles and over many years. It started with the earmuff which is still very relevant and addresses very noisy environments (e.g. airports, construction, shooting) or complex working/communication situations (e.g. fighter pilots). Over the years development of biocompatible soft materials has enabled soft earplugs in different styles and colors as well as recent development of “one fits many” standard semi-soft earplugs in silicon-rubber type materials. For severe situations even the combination of an earmuff and an “in-the-ear” HPD is required to achieve desired attenuation. The physical limitation of hearing protection based on ear worn devices is defined where bone-conduction (body acoustics) becomes dominant at around 40 dB attenuation.
A common disadvantage of the above mentioned HPD styles is wearing discomfort. In case of the earmuffs, they are large which creates difficulties in combination with other head worn gear and they “close off” the ear too much for most applications. The in-the-ear styles mentioned are devices made to fit “the average” ear in one way or the other. Either the fit is provided by softness of the material which leads to undefined device insertion and undefined attenuation, or the fit is provided by standard shaped structures intended to block off the ear canal. In both cases the flat distribution of the individual shape of the outer ear and the ear canal leads to bad fit, pressure points in the ear and undefined positioning of the device.
To address this wearing comfort issue, in-the-ear hearing aid technology has been applied making customized ear molds with passive acoustical filter. These are long lasting devices with good wearing comfort. However, this customization process is traditionally a very manual process creating varying results over time, low reproducibility and the quality is very operator skill dependent.
In order to overcome all of the above mentioned disadvantages a novel technique is proposed. The basic idea is to use rapid prototyping technology in a manufacturing environment as described, for example, in U.S. Pat. No. 6,533,062 B1 or U.S. 2003/0133583 A1. This technique is successfully being used in hearing aids and can be applied in a similar fashion for HPDs. By doing this, a whole new range of features and functions become feasible for HPDs.
The idea to use rapid prototyping technology, such as layer-by-layer laser sintering, in manufacturing shells, primarily for hearing aids, is described, for example, in U.S. Pat. No. 6,533,062 B1 or U.S. 2003/0133583 A1.
Passive hearing protection devices (HPDs) allowing controlled sound attenuation exist in several forms.
In spite of a certain frequency dependant sound amplitude damping achieved by some known passive HPDs, it is a fundamental property of all these devices that a higher sound attenuation of a hearing protection device will reduce the communication ability with the surroundings. The attempts of the prior art to solve this problem, namely to configure the frequency selective sound attenuation such as to retain a high dynamic in speech or voice frequencies, have failed because of the stringent requirements set up by the high noise concentration at certain working places and in the military area, for example, so that the worker, employee or soldier must temporarily remove the hearing protection device if he wants to hear persons talking to him.
U.S. Pat. No. 6,148,821 discloses a selective non-linear attenuating earplug consisting of a shell and a noise attenuation button. The button comprises a hollow stem which is inserted into a mating cylindrical outer opening of the shell. The hollow stem and the cylindrical wall of the outer opening of the shell both have a radially extending hole, which may be aligned by rotating the stem relative to the shell. The distal end of the hollow stem is provided with a sound attenuation filter connecting the interior of the hollow stem with a sound bore within said shell communicating with the user's ear canal. When the two holes are aligned, sound may enter through the opening into the interior of the hollow stem, pass through the filter and reach, attenuated by the filter, the ear canal. However, this approach does not afford non-attenuated sound communication and lacks convenient and safe operation by the user, since the button has to be reset manually and the button has to be rotated.
Further, active hearing protection devices are generally known which include a microphone, an audio signal processing unit, such as an amplifier, and a speaker for frequency-selective or temporary by-passing of the acoustic attenuation filter function provided by the earplug, for example, in order to enable acoustic communication with other persons in noisy environments.
Hearing protection earplugs having a customized shell are known, for example, from U.S. Pat. No. 6,533,062 B1. For manufacturing customized earplugs first the inner shape of the user's outer ear and ear canal is measured, for example by three-dimensional laser scanning or by forming an impression of the ear which subsequently undergoes three-dimensional (3D) laser scanning. The desired outer shape of the shell is determined from the measured shape of the user's ear for achieving optimized fit within the ear canal and outer ear. The shell can be produced by an incremental build-up process such as layer-by-layer laser sintering of a powder material, whereby a relatively hard shell is achieved which has an optimized fit within the user's ear.
It is an object of the invention to provide for a passive hearing protection earplug, which is adapted for enabling acoustic communication of the user with other persons without the need to remove the earplug from the ear, while nevertheless maintaining a simple construction of the earplug. It is a further object of the invention to provide for a use of such an earplug and to provide for a method for manufacturing such an earplug.